// MIT License

// Copyright (c) 2019 Erin Catto

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#include "test.h"

// This test shows how to apply forces and torques to a body.
// It also shows how to use the friction joint that can be useful
// for overhead games.
class ApplyForce : public Test
{
public:
  ApplyForce()
  {
    m_world->SetGravity(b2Vec2(0.0f, 0.0f));

    const float k_restitution = 0.4f;

    b2Body* ground;
    {
      b2BodyDef bd;
      bd.position.Set(0.0f, 20.0f);
      ground = m_world->CreateBody(&bd);

      b2EdgeShape shape;

      b2FixtureDef sd;
      sd.shape = &shape;
      sd.density = 0.0f;
      sd.restitution = k_restitution;

      // Left vertical
      shape.SetTwoSided(b2Vec2(-20.0f, -20.0f), b2Vec2(-20.0f, 20.0f));
      ground->CreateFixture(&sd);

      // Right vertical
      shape.SetTwoSided(b2Vec2(20.0f, -20.0f), b2Vec2(20.0f, 20.0f));
      ground->CreateFixture(&sd);

      // Top horizontal
      shape.SetTwoSided(b2Vec2(-20.0f, 20.0f), b2Vec2(20.0f, 20.0f));
      ground->CreateFixture(&sd);

      // Bottom horizontal
      shape.SetTwoSided(b2Vec2(-20.0f, -20.0f), b2Vec2(20.0f, -20.0f));
      ground->CreateFixture(&sd);
    }

    {
      b2Transform xf1;
      xf1.q.Set(0.3524f * b2_pi);
      xf1.p = xf1.q.GetXAxis();

      b2Vec2 vertices[3];
      vertices[0] = b2Mul(xf1, b2Vec2(-1.0f, 0.0f));
      vertices[1] = b2Mul(xf1, b2Vec2(1.0f, 0.0f));
      vertices[2] = b2Mul(xf1, b2Vec2(0.0f, 0.5f));
      
      b2PolygonShape poly1;
      poly1.Set(vertices, 3);

      b2FixtureDef sd1;
      sd1.shape = &poly1;
      sd1.density = 2.0f;

      b2Transform xf2;
      xf2.q.Set(-0.3524f * b2_pi);
      xf2.p = -xf2.q.GetXAxis();

      vertices[0] = b2Mul(xf2, b2Vec2(-1.0f, 0.0f));
      vertices[1] = b2Mul(xf2, b2Vec2(1.0f, 0.0f));
      vertices[2] = b2Mul(xf2, b2Vec2(0.0f, 0.5f));
      
      b2PolygonShape poly2;
      poly2.Set(vertices, 3);

      b2FixtureDef sd2;
      sd2.shape = &poly2;
      sd2.density = 2.0f;

      b2BodyDef bd;
      bd.type = b2_dynamicBody;

      bd.position.Set(0.0f, 3.0);
      bd.angle = b2_pi;
      bd.allowSleep = false;
      m_body = m_world->CreateBody(&bd);
      m_body->CreateFixture(&sd1);
      m_body->CreateFixture(&sd2);

      float gravity = 10.0f;
      float I = m_body->GetInertia();
      float mass = m_body->GetMass();

      // Compute an effective radius that can be used to
      // set the max torque for a friction joint
      // For a circle: I = 0.5 * m * r * r ==> r = sqrt(2 * I / m)
      float radius = b2Sqrt(2.0f * I / mass);

      b2FrictionJointDef jd;
      jd.bodyA = ground;
      jd.bodyB = m_body;
      jd.localAnchorA.SetZero();
      jd.localAnchorB = m_body->GetLocalCenter();
      jd.collideConnected = true;
      jd.maxForce = 0.5f * mass * gravity;
      jd.maxTorque = 0.2f * mass * radius * gravity;

      m_world->CreateJoint(&jd);
    }

    {
      b2PolygonShape shape;
      shape.SetAsBox(0.5f, 0.5f);

      b2FixtureDef fd;
      fd.shape = &shape;
      fd.density = 1.0f;
      fd.friction = 0.3f;

      for (int i = 0; i < 10; ++i)
      {
        b2BodyDef bd;
        bd.type = b2_dynamicBody;

        bd.position.Set(0.0f, 7.0f + 1.54f * i);
        b2Body* body = m_world->CreateBody(&bd);

        body->CreateFixture(&fd);

        float gravity = 10.0f;
        float I = body->GetInertia();
        float mass = body->GetMass();

        // For a circle: I = 0.5 * m * r * r ==> r = sqrt(2 * I / m)
        float radius = b2Sqrt(2.0f * I / mass);

        b2FrictionJointDef jd;
        jd.localAnchorA.SetZero();
        jd.localAnchorB.SetZero();
        jd.bodyA = ground;
        jd.bodyB = body;
        jd.collideConnected = true;
        jd.maxForce = mass * gravity;
        jd.maxTorque = 0.1f * mass * radius * gravity;

        m_world->CreateJoint(&jd);
      }
    }
  }

  void Step(Settings& settings) override
  {
    g_debugDraw.DrawString(5, m_textLine, "Forward (W), Turn (A) and (D)");
    m_textLine += m_textIncrement;

    if (glfwGetKey(g_mainWindow, GLFW_KEY_W) == GLFW_PRESS)
    {
      b2Vec2 f = m_body->GetWorldVector(b2Vec2(0.0f, -50.0f));
      b2Vec2 p = m_body->GetWorldPoint(b2Vec2(0.0f, 3.0f));
      m_body->ApplyForce(f, p, true);
    }

    if (glfwGetKey(g_mainWindow, GLFW_KEY_A) == GLFW_PRESS)
    {
      m_body->ApplyTorque(10.0f, true);
    }

    if (glfwGetKey(g_mainWindow, GLFW_KEY_D) == GLFW_PRESS)
    {
      m_body->ApplyTorque(-10.0f, true);
    }

    Test::Step(settings);
  }

  static Test* Create()
  {
    return new ApplyForce;
  }

  b2Body* m_body;
};

static int testIndex = RegisterTest("Forces", "Apply Force", ApplyForce::Create);
